ray();

	foreach ( $registered_meta as $name => $args ) {
		if ( $args['revisions_enabled'] ) {
			$wp_revisioned_meta_keys[ $name ] = true;
		}
	}

	$wp_revisioned_meta_keys = array_keys( $wp_revisioned_meta_keys );

	/**
	 * Filter the list of post meta keys to be revisioned.
	 *
	 * @since 6.4.0
	 *
	 * @param array  $keys      An array of meta fields to be revisioned.
	 * @param string $post_type The post type being revisioned.
	 */
	return apply_filters( 'wp_post_revision_meta_keys', $wp_revisioned_meta_keys, $post_type );
}

/**
 * Check whether revisioned post meta fields have changed.
 *
 * @since 6.4.0
 *
 * @param bool    $post_has_changed Whether the post has changed.
 * @param WP_Post $last_revision    The last revision post object.
 * @param WP_Post $post             The post object.
 * @return bool Whether the post has changed.
 */
function wp_check_revisioned_meta_fields_have_changed( $post_has_changed, WP_Post $last_revision, WP_Post $post ) {
	foreach ( wp_post_revision_meta_keys( $post->post_type ) as $meta_key ) {
		if ( get_post_meta( $post->ID, $meta_key ) !== get_post_meta( $last_revision->ID, $meta_key ) ) {
			$post_has_changed = true;
			break;
		}
	}
	return $post_has_changed;
}

/**
 * Deletes a revision.
 *
 * Deletes the row from the posts table corresponding to the specified revision.
 *
 * @since 2.6.0
 *
 * @param int|WP_Post $revision Revision ID or revision object.
 * @return WP_Post|false|null Null or false if error, deleted post object if success.
 */
function wp_delete_post_revision( $revision ) {
	$revision = wp_get_post_revision( $revision );

	if ( ! $revision ) {
		return $revision;
	}

	$delete = wp_delete_post( $revision->ID );

	if ( $delete ) {
		/**
		 * Fires once a post revision has been deleted.
		 *
		 * @since 2.6.0
		 *
		 * @param int     $revision_id Post revision ID.
		 * @param WP_Post $revision    Post revision object.
		 */
		do_action( 'wp_delete_post_revision', $revision->ID, $revision );
	}

	return $delete;
}

/**
 * Returns all revisions of specified post.
 *
 * @since 2.6.0
 *
 * @see get_children()
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.
 * @param array|null  $args Optional. Arguments for retrieving post revisions. Default null.
 * @return WP_Post[]|int[] Array of revision objects or IDs, or an empty array if none.
 */
function wp_get_post_revisions( $post = 0, $args = null ) {
	$post = get_post( $post );

	if ( ! $post || empty( $post->ID ) ) {
		return array();
	}

	$defaults = array(
		'order'         => 'DESC',
		'orderby'       => 'date ID',
		'check_enabled' => true,
	);
	$args     = wp_parse_args( $args, $defaults );

	if ( $args['check_enabled'] && ! wp_revisions_enabled( $post ) ) {
		return array();
	}

	$args = array_merge(
		$args,
		array(
			'post_parent' => $post->ID,
			'post_type'   => 'revision',
			'post_status' => 'inherit',
		)
	);

	$revisions = get_children( $args );

	if ( ! $revisions ) {
		return array();
	}

	return $revisions;
}

/**
 * Returns the latest revision ID and count of revisions for a post.
 *
 * @since 6.1.0
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
 * @return array|WP_Error {
 *     Returns associative array with latest revision ID and total count,
 *     or a WP_Error if the post does not exist or revisions are not enabled.
 *
 *     @type int $latest_id The latest revision post ID or 0 if no revisions exist.
 *     @type int $count     The total count of revisions for the given post.
 * }
 */
function wp_get_latest_revision_id_and_total_count( $post = 0 ) {
	$post = get_post( $post );

	if ( ! $post ) {
		return new WP_Error( 'invalid_post', __( 'Invalid post.' ) );
	}

	if ( ! wp_revisions_enabled( $post ) ) {
		return new WP_Error( 'revisions_not_enabled', __( 'Revisions not enabled.' ) );
	}

	$args = array(
		'post_parent'         => $post->ID,
		'fields'              => 'ids',
		'post_type'           => 'revision',
		'post_status'         => 'inherit',
		'order'               => 'DESC',
		'orderby'             => 'date ID',
		'posts_per_page'      => 1,
		'ignore_sticky_posts' => true,
	);

	$revision_query = new WP_Query();
	$revisions      = $revision_query->query( $args );

	if ( ! $revisions ) {
		return array(
			'latest_id' => 0,
			'count'     => 0,
		);
	}

	return array(
		'latest_id' => $revisions[0],
		'count'     => $revision_query->found_posts,
	);
}

/**
 * Returns the url for viewing and potentially restoring revisions of a given post.
 *
 * @since 5.9.0
 *
 * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global `$post`.
 * @return string|null The URL for editing revisions on the given post, otherwise null.
 */
function wp_get_post_revisions_url( $post = 0 ) {
	$post = get_post( $post );

	if ( ! $post instanceof WP_Post ) {
		return null;
	}

	// If the post is a revision, return early.
	if ( 'revision' === $post->post_type ) {
		return get_edit_post_link( $post );
	}

	if ( ! wp_revisions_enabled( $post ) ) {
		return null;
	}

	$revisions = wp_get_latest_revision_id_and_total_count( $post->ID );

	if ( is_wp_error( $revisions ) || 0 === $revisions['count'] ) {
		return null;
	}

	return get_edit_post_link( $revisions['latest_id'] );
}

/**
 * Determines whether revisions are enabled for a given post.
 *
 * @since 3.6.0
 *
 * @param WP_Post $post The post object.
 * @return bool True if number of revisions to keep isn't zero, false otherwise.
 */
function wp_revisions_enabled( $post ) {
	return wp_revisions_to_keep( $post ) !== 0;
}

/**
 * Determines how many revisions to retain for a given post.
 *
 * By default, an infinite number of revisions are kept.
 *
 * The constant WP_POST_REVISIONS can be set in wp-config to specify the limit
 * of revisions to keep.
 *
 * @since 3.6.0
 *
 * @param WP_Post $post The post object.
 * @return int The number of revisions to keep.
 */
function wp_revisions_to_keep( $post ) {
	$num = WP_POST_REVISIONS;

	if ( true === $num ) {
		$num = -1;
	} else {
		$num = (int) $num;
	}

	if ( ! post_type_supports( $post->post_type, 'revisions' ) ) {
		$num = 0;
	}

	/**
	 * Filters the number of revisions to save for the given post.
	 *
	 * Overrides the value of WP_POST_REVISIONS.
	 *
	 * @since 3.6.0
	 *
	 * @param int     $num  Number of revisions to store.
	 * @param WP_Post $post Post object.
	 */
	$num = apply_filters( 'wp_revisions_to_keep', $num, $post );

	/**
	 * Filters the number of revisions to save for the given post by its post type.
	 *
	 * Overrides both the value of WP_POST_REVISIONS and the {@see 'wp_revisions_to_keep'} filter.
	 *
	 * The dynamic portion of the hook name, `$post->post_type`, refers to
	 * the post type slug.
	 *
	 * Possible hook names include:
	 *
	 *  - `wp_post_revisions_to_keep`
	 *  - `wp_page_revisions_to_keep`
	 *
	 * @since 5.8.0
	 *
	 * @param int     $num  Number of revisions to store.
	 * @param WP_Post $post Post object.
	 */
	$num = apply_filters( "wp_{$post->post_type}_revisions_to_keep", $num, $post );

	return (int) $num;
}

/**
 * Sets up the post object for preview based on the post autosave.
 *
 * @since 2.7.0
 * @access private
 *
 * @param WP_Post $post
 * @return WP_Post|false
 */
function _set_preview( $post ) {
	if ( ! is_object( $post ) ) {
		return $post;
	}

	$preview = wp_get_post_autosave( $post->ID );

	if ( is_object( $preview ) ) {
		$preview = sanitize_post( $preview );

		$post->post_content = $preview->post_content;
		$post->post_title   = $preview->post_title;
		$post->post_excerpt = $preview->post_excerpt;
	}

	add_filter( 'get_the_terms', '_wp_preview_terms_filter', 10, 3 );
	add_filter( 'get_post_metadata', '_wp_preview_post_thumbnail_filter', 10, 3 );
	add_filter( 'get_post_metadata', '_wp_preview_meta_filter', 10, 4 );

	return $post;
}

/**
 * Filters the latest content for preview from the post autosave.
 *
 * @since 2.7.0
 * @access private
 */
function _show_post_preview() {
	if ( isset( $_GET['preview_id'] ) && isset( $_GET['preview_nonce'] ) ) {
		$id = (int) $_GET['preview_id'];

		if ( false === wp_verify_nonce( $_GET['preview_nonce'], 'post_preview_' . $id ) ) {
			wp_die( __( 'Sorry, you are not allowed to preview drafts.' ), 403 );
		}

		add_filter( 'the_preview', '_set_preview' );
	}
}

/**
 * Filters terms lookup to set the post format.
 *
 * @since 3.6.0
 * @access private
 *
 * @param array  $terms
 * @param int    $post_id
 * @param string $taxonomy
 * @return array
 */
function _wp_preview_terms_filter( $terms, $post_id, $taxonomy ) {
	$post = get_post();

	if ( ! $post ) {
		return $terms;
	}

	if ( empty( $_REQUEST['post_format'] ) || $post->ID !== $post_id
		|| 'post_format' !== $taxonomy || 'revision' === $post->post_type
	) {
		return $terms;
	}

	if ( 'standard' === $_REQUEST['post_format'] ) {
		$terms = array();
	} else {
		$term = get_term_by( 'slug', 'post-format-' . sanitize_key( $_REQUEST['post_format'] ), 'post_format' );

		if ( $term ) {
			$terms = array( $term ); // Can only have one post format.
		}
	}

	return $terms;
}

/**
 * Filters post thumbnail lookup to set the post thumbnail.
 *
 * @since 4.6.0
 * @access private
 *
 * @param null|array|string $value    The value to return - a single metadata value, or an array of values.
 * @param int               $post_id  Post ID.
 * @param string            $meta_key Meta key.
 * @return null|array The default return value or the post thumbnail meta array.
 */
function _wp_preview_post_thumbnail_filter( $value, $post_id, $meta_key ) {
	$post = get_post();

	if ( ! $post ) {
		return $value;
	}

	if ( empty( $_REQUEST['_thumbnail_id'] ) || empty( $_REQUEST['preview_id'] )
		|| $post->ID !== $post_id || $post_id !== (int) $_REQUEST['preview_id']
		|| '_thumbnail_id' !== $meta_key || 'revision' === $post->post_type
	) {
		return $value;
	}

	$thumbnail_id = (int) $_REQUEST['_thumbnail_id'];

	if ( $thumbnail_id <= 0 ) {
		return '';
	}

	return (string) $thumbnail_id;
}

/**
 * Gets the post revision version.
 *
 * @since 3.6.0
 * @access private
 *
 * @param WP_Post $revision
 * @return int|false
 */
function _wp_get_post_revision_version( $revision ) {
	if ( is_object( $revision ) ) {
		$revision = get_object_vars( $revision );
	} elseif ( ! is_array( $revision ) ) {
		return false;
	}

	if ( preg_match( '/^\d+-(?:autosave|revision)-v(\d+)$/', $revision['post_name'], $matches ) ) {
		return (int) $matches[1];
	}

	return 0;
}

/**
 * Upgrades the revisions author, adds the current post as a revision and sets the revisions version to 1.
 *
 * @since 3.6.0
 * @access private
 *
 * @global wpdb $wpdb WordPress database abstraction object.
 *
 * @param WP_Post $post      Post object.
 * @param array   $revisions Current revisions of the post.
 * @return bool true if the revisions were upgraded, false if problems.
 */
function _wp_upgrade_revisions_of_post( $post, $revisions ) {
	global $wpdb;

	// Add post option exclusively.
	$lock   = "revision-upgrade-{$post->ID}";
	$now    = time();
	$result = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO `$wpdb->options` (`option_name`, `option_value`, `autoload`) VALUES (%s, %s, 'off') /* LOCK */", $lock, $now ) );

	if ( ! $result ) {
		// If we couldn't get a lock, see how old the previous lock is.
		$locked = get_option( $lock );

		if ( ! $locked ) {
			/*
			 * Can't write to the lock, and can't read the lock.
			 * Something broken has happened.
			 */
			return false;
		}

		if ( $locked > $now - HOUR_IN_SECONDS ) {
			// Lock is not too old: some other process may be upgrading this post. Bail.
			return false;
		}

		// Lock is too old - update it (below) and continue.
	}

	// If we could get a lock, re-"add" the option to fire all the correct filters.
	update_option( $lock, $now );

	reset( $revisions );
	$add_last = true;

	do {
		$this_revision = current( $revisions );
		$prev_revision = next( $revisions );

		$this_revision_version = _wp_get_post_revision_version( $this_revision );

		// Something terrible happened.
		if ( false === $this_revision_version ) {
			continue;
		}

		/*
		 * 1 is the latest revision version, so we're already up to date.
		 * No need to add a copy of the post as latest revision.
		 */
		if ( 0 < $this_revision_version ) {
			$add_last = false;
			continue;
		}

		// Always update the revision version.
		$update = array(
			'post_name' => preg_replace( '/^(\d+-(?:autosave|revision))[\d-]*$/', '$1-v1', $this_revision->post_name ),
		);

		/*
		 * If this revision is the oldest revision of the post, i.e. no $prev_revision,
		 * the correct post_author is probably $post->post_author, but that's only a good guess.
		 * Update the revision version only and Leave the author as-is.
		 */
		if ( $prev_revision ) {
			$prev_revision_version = _wp_get_post_revision_version( $prev_revision );

			// If the previous revision is already up to date, it no longer has the information we need :(
			if ( $prev_revision_version < 1 ) {
				$update['post_author'] = $prev_revision->post_author;
			}
		}

		// Upgrade this revision.
		$result = $wpdb->update( $wpdb->posts, $update, array( 'ID' => $this_revision->ID ) );

		if ( $result ) {
			wp_cache_delete( $this_revision->ID, 'posts' );
		}
	} while ( $prev_revision );

	delete_option( $lock );

	// Add a copy of the post as latest revision.
	if ( $add_last ) {
		wp_save_post_revision( $post->ID );
	}

	return true;
}

/**
 * Filters preview post meta retrieval to get values from the autosave.
 *
 * Filters revisioned meta keys only.
 *
 * @since 6.4.0
 *
 * @param mixed  $value     Meta value to filter.
 * @param int    $object_id Object ID.
 * @param string $meta_key  Meta key to filter a value for.
 * @param bool   $single    Whether to return a single value.
 * @return mixed Original meta value if the meta key isn't revisioned, the object doesn't exist,
 *               the post type is a revision or the post ID doesn't match the object ID.
 *               Otherwise, the revisioned meta value is returned for the preview.
 */
function _wp_preview_meta_filter( $value, $object_id, $meta_key, $single ) {
	$post = get_post();

	if ( empty( $post )
		|| $post->ID !== $object_id
		|| ! in_array( $meta_key, wp_post_revision_meta_keys( $post->post_type ), true )
		|| 'revision' === $post->post_type
	) {
		return $value;
	}

	$preview = wp_get_post_autosave( $post->ID );

	if ( false === $preview ) {
		return $value;
	}

	return get_post_meta( $preview->ID, $meta_key, $single );
}